Two rottweilers killed an 83-year-old man in Alabama. A 2-day-old infant was mauled to death in Pennsylvania. A 2-year-old girl died after she was bitten by a pit bull in West Virginia.

Jim Crosby has worked all of these cases as a canine crime scene investigator.

The retired Jacksonville sheriff's lieutenant relies on forensic tools such as bite molds and measurements, necropsy results and saline swabs. His goal: to determine why a dog mauled a person and whether it should be rehabilitated or destroyed because of its behavior.

"I speak dog," said the 54-year-year-old Crosby, who lives with three curly-coated retrievers and two miniature wirehaired dachshunds. "No, it's not whispering. There's no whispering involved."

Dog bites are often much more complex than they appear, and they shouldn't be handled with a knee-jerk reaction of instantly killing the dog, Crosby said.

Among the few forensic experts on dog bites in the country, Crosby is writing a book called "Working the Worst: A Guide to Investigating Dog Related Fatalities." It's intended as a manual for detectives and animal officers.

There aren't many in his line of work. Two men in California provide forensic evaluations and expert testimony during cases, and both are animal behavior experts. Crosby differs because he comes from a traditional law enforcement background.

His second career began soon after he retired in 1999 after 22 years with the Jacksonville Sheriff's Office. First he became a trainer. Then he started thinking about dog behavior and realized there weren't any standardized law enforcement investigation procedures for dog bites.

Now he travels the country to help animal control departments, lawyers and police agencies with dog-mauling investigations. He's worked on 17 fatal dog-bite cases in recent years, paying his own way for some of those first consulting jobs. Now, he's getting paid by animal shelters, prosecutors and even defense attorneys to investigate. But he'd like to find a university, insurance company or other business that will pay him to do research and forensic work.

Through his work, Crosby met Victoria Stilwell, a dog trainer and host of cable channel Animal Planet's "It's Me or the Dog," and a friendship blossomed. The two are scheduled to give presentations at the National Dog Bite Awareness Conference in Denver on Friday.

"I'm more like his nurse, where I hand him the stuff, the saline and the swabs," Stilwell said recently on her weekly podcast. "Where he and I really work well together is that we watch the dog's behavior. We really find out why. What was in the dog's circumstance that made this dog do this?"

The cases Crosby investigates are often grim. In many, the offending dogs haven't been properly socialized or trained, and the victims are often children. So far this year, 27 fatal dog bite cases have been reported nationwide and thousands more nonlethal bites.

"It's usually a perfect storm of things," he said. "Most commonly, there's some kind of human failure."

He is currently working the case of an 83-year-old man in Leeds, Ala., who was killed by his neighbor's two rottweilers.

Crosby is helping police and prosecutors build a manslaughter case against the dogs' owner, who was found to have 33 other rottweilers on his property. Crosby has looked at photos of the attack, interviewed witnesses and analyzed necropsy results of the two responsible dogs, which were shot by officers after the attack.

In 2005, Crosby helped authorities prosecute a West Virginia man whose pit bull killed a 2-year-old girl. It was the first time a person in that state had been convicted of involuntary manslaughter as a result of a dog attack. Crosby found the dog had been improperly cared for, poorly trained and not adequately socialized. He said the owner also encouraged aggressive behavior that led the dog to bite five adults before the fatal attack.

"These are specialized kinds of homicides," he said. "But the weapon is a semi-sentient being operating both under a person's direction and somewhat on its own."

Sometimes, Crosby's evaluations don't involve a death. In September, he evaluated a pit bull named Memphis in Bloomfield, N.J. The dog was picked up off the streets by the local animal shelter. A resident who is a dog trainer spent several days training Memphis in his home and wanted to adopt him - but the shelter didn't believe the dog was ready for adoption, and Crosby agreed.

Crosby, who was paid by the township to evaluate the dog, said he thinks Memphis can be adopted with some additional training, but is "not ready for a run at an average Joe Blow home" either.

This year, Crosby was called to McKeesport, Pa., after a 2-day-old boy was fatally mauled. The baby's mother had left the infant in a carrier. A husky named Helo and a pit bull were loose in the house, and two other dogs were in the basement. Prosecutors thought Helo had killed the baby and a judge ruled that the dog should be put down, but the man who adopted the dog after the attack appealed.

Crosby found that investigators seized Helo and the pit bull but didn't look at the behavior of the other two dogs. He added that when he evaluated Helo, the dog was "personable, friendly and nonthreatening."

Pam Amicarella, the attorney representing Helo, said they trusted Crosby's assessment and would also have put the dog to sleep if he had recommended it. Instead, Helo was sent to live at an animal sanctuary.

"If he had determined the dog was aggressive or dangerous, we agreed the dog would be put down," she said. "He was able, because of his background, to put together an opinion of what had occurred at the scene."

The other three dogs are still living in the community, which dismays Crosby because those dogs could have been involved in the attack.

"This case shows that you can't make assumptions and that you have to check everything carefully," he said. "Hopefully these other three dogs that are unaccounted for won't hurt anyone else."